Light absorption and scattering by a photolayer with closely packed particles

Light absorption and scattering by weakly absorbing layers of close-packed fine-grained silver halide particles was studied. Absorption characteristics of an elementary volume and a photolayer were found to have a nonlinear and nonmonotonic dependence on the concentration. Qualitative specific features of this dependence in the range of medium values of volume concentrations from 0.4 to 0.8 were expressed by an empirical formula. The average cosine of the depth brightness diagram and the probability of photon survival Λ in a concentrated photolayer were calculated. The analysis of changes in Λ in a close-packed medium in a more general case, irrespective of the size and the degree of absorption of particles, was carried out. A conclusion was made concerning the character of changes in the scattering indicatrix of a photolayer caused by an increase of its density.     

Light scattering by groups of spherical particles

Light scattering by groups of spherical particles is considered. It is shown that the structure of the groups and their orientational distribution can be judged from the spectrum and polarization of the scattered light. Syktyvkar State University, 55, Oktyabr'skii Ave., Syktyvkar, 167001, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 228–231, March–April, 1997.     

Light scattering and absorption by densely packed groups of spherical particles

Light scattering by clusters of spheres is investigated using numerical light scattering simulations. We consider clusters with density of 0.1-30%. Simulations are carried out for various real part of refractive indices (i.e., 1.01, 1.10, 1.31, 1.60, and 2.00) and for two values of the imaginary part of the refractive index (0 and 0.01) of spheres in the cluster. All spheres in the cluster have the same size (kr=4, k=2π/λ, r is the radius of the sphere, λ is the wavelength of the incident light).The obtained results include behaviors of cross sections as functions of densities (up to 30%), investigation of the influence of multiple scattering inside the media on the cross sections, and influence of densities on phase matrix elements (PMEs) and parameters obtained from the PMEs such as the cross polarization ratio, degree of linear depolarization, entropy, etc.In addition, we also investigate the influence of particle size for the same total volume of the cluster on cross sections. The outer radius R of the cluster of spheres was constant and equal to 40/k in all calculations.     

Light scattering by needle-type and disk-type particles

A powerful tool to analyze light scattering by 3D arbitrary-shaped homogeneous or inhomogeneous obstacles located in free space is based on volume integral equation. In this paper we apply a weak form of volume integral equation to simulate light scattering by needle- and disk-type particles such as straight and curved cylinders, cylindrical plate and hexagonal prism with high aspect ratio and low and high values of refractive indexes. For problems where discrete sources method could be applied, we calculated differential scattering cross-section using both methods and got excellent agreement in results.     

Light scattering by a spherical particle with multiple densely packed inclusions

This paper calculates light scattering by a spherical water particle containing densely packed inclusions at a visible wavelength 0.55 \mum by a combination of ray-tracing and Monte Carlo techniques. While the individual reflection and refraction events at the outer boundary of a sphere particle are considered by a ray-tracing program, the Monte Carlo routine simulates internal scattering processes. The main advantage of this method is that the shape of the particle can be arbitrary, and multiple scattering can be considered in the internal scattering processes. A dense-medium light-scattering theory based on the introduction of the static structure factor is used to calculate the phase function and asymmetry parameters for densely packed inclusions. Numerical results of the single scattering characteristics for a sphere containing multiple densely packed inclusions are given.     

含有密集随机分布内核的椭球粒子光散射特性研究

给出了一种结合射线追踪和蒙特卡罗方法计算含核粒子光散射的方法,内核粒子可以为稀疏分布也可为浓密分布.粒子外边界的反射和折射由射线追踪方法计算,而粒子内部的多次散射过程由蒙特卡罗方法模拟;当内核粒子为浓密随机分布时,其单次散射特性由基于静态结构因子（static structure factor）的浓密介质光散射理论计算.最后讨论了含核椭球粒子模型的单次散射特性. 关键词： 射线追踪技术 蒙特卡洛方法 光散射 椭球粒子     

Light scattering by fluffy particles with the PROGRA experiment: Mixtures of materials

The PROGRA² experiment is specifically designed to measure the linear polarization of the light scattered by clouds of particles. The imaging method allows us to obtain maps of polarization and to measure the size distribution and the number density of the particles in the field of view. This work presents a systematic study of highly porous (fluffy) aggregates with submicron-sized constituent grains lifted by an air-draught. The main materials are silica and carbon. The maximum in polarization mainly depends on the average size of the constituent grains. The results, mainly concerned with the negative branch of the phase curves, the maximum polarization, the color effect and the albedo are compared with cometary observations and discussed in terms of physical properties.     

基片与多形态缺陷粒子的复合光散射

为了给基片无损检测工程提供强有力的理论基础,提出三种形态的缺陷粒子散射模型。针对基片与缺陷粒子的半空间问题,吸收边界使用了广义完全匹配吸收层,结合三波技术引入激励源给出相应的连接边界条件并将互易性定理应用到近远场外推中使过程简化。数值计算给出了镶嵌于基片中的多种几何体Cu和SiO2缺陷粒子的散射场的角分布及p偏振和s偏振下镶嵌Cu球体粒子的电场分布。结果显示：角分布和场分布跟粒子形态关系密切。椭球体散射场的震荡明显比柱体场震荡激烈。在s偏振下电场强度分布差值极小,不利于通过分析场值分布特点反演缺陷特征值。因此建议工程上使用p偏振光对基片进行无损检测。     

随机取向群聚椭球粒子光散射特性研究

利用离散偶极子近似方法,考虑单元粒子之间的电磁相互作用,数值计算了随机取向的不同尺度参数、不同纵横比的群聚椭球粒子的缪勒矩阵元素,给出了各个缪勒矩阵元素的角分布曲线,探讨了随机取向的群聚椭球粒子的尺度参数、纵横比、基本粒子相对位置对其缪勒矩阵元素的影响。并将随机取向群聚椭球粒子的光散射特性与单个等效球形粒子的数值结果进行了比较。结果表明,随机取向群聚椭球粒子的光散射特性与等效球形粒子的光散射特性存在很大差别,基本粒子的形状越偏离球形,这种差别就越大; 随机取向群聚椭球粒子中椭球粒子的纵横比和相对位置对整个群聚粒子的缪勒矩阵元素存在不同程度的影响,并且此影响随着粒子尺度参数的增大而变得更加显著。     

随机取向群聚椭球粒子光散射特性研究

利用离散偶极子近似方法,考虑单元粒子之间的电磁相互作用,数值计算了随机取向的不同尺度参数、不同纵横比的群聚椭球粒子的缪勒矩阵元素,给出了各个缪勒矩阵元素的角分布曲线,探讨了随机取向的群聚椭球粒子的尺度参数、纵横比、基本粒子相对位置对其缪勒矩阵元素的影响。并将随机取向群聚椭球粒子的光散射特性与单个等效球形粒子的数值结果进行了比较。结果表明,随机取向群聚椭球粒子的光散射特性与等效球形粒子的光散射特性存在很大差别,基本粒子的形状越偏离球形,这种差别就越大; 随机取向群聚椭球粒子中椭球粒子的纵横比和相对位置对整个群聚粒子的缪勒矩阵元素存在不同程度的影响,并且此影响随着粒子尺度参数的增大而变得更加显著。     

Difference scattering field properties between periodic defect particles and three-dimensional slightly rough optical surface

Based on the practical situation of nondestructive examination, the calculation model of the composite scattering is established by using a three-dimensional half-space finite difference time domain, and the Monte Carlo method is used to solve the problem of the optical surface with roughness in the proposed scheme. Moreover, the defect particles are observed as periodic particles for a more complex situation. In order to obtain the scattering contribution of defects inside the optical surface, a difference radar cross section is added into the model to analyze the selected calculations on the effects of numbers, separation distances, different depths and different materials of defects. The effects of different incident angles are also discussed. The numerical results are analyzed in detail to demonstrate the best position to find the defects in the optical surface by detecting in steps of a fixed degree for the incident angle.     

水中密排圆柱体群的超声多重散射参数

以水中紧密排列的平行圆柱体群为对象,研究平面超声脉冲经多重散射后的透射波性质,通过分析其中头波和散射波的特征获得对应的多重散射参数.对直径随机分布、位置无序排列、数量密度约100个/cm²、面积占空比约0.53的非接触圆柱体群,采用中心频率2.5 MHz的宽带脉冲波入射。为解决透射信号在时域表现出随机性的问题,将散射体尺寸、分布都相同但位置分布不同的多个模型仿真的透射波叠加平均后用于分析.在频域对头波的宽带衰减系数进行分析,并在时域研究散射波声强的时间演化曲线,获得了系统的弹性平均自由程、传输平均自由程等多重散射参数。经多重散射后,透射波中的头波表现出相干性,由不相干近似理论可对其对应的散射参数进行定性描述;散射波是不相干的,其对应的多重散射参数可近似利用扩散近似理论获得。     

Light scattering by “soft” particles of arbitrary shape and size: II—Arbitrary orientation of particles in the space

In this part of the article a new version analysis of light scattering by “soft” particles is presented that makes it possible to reduce and simplify the process of numerical calculations. The calculation results of the integral scattering cross-sections and indicatrices for spheroid, parallelepiped and cylinder for their arbitrary orientation in space are given as an illustration. The results are accompanied by transparent physical interpretations, based on the examination of the contour graphs of the three-dimensional spectra of particles.     

Light scattering by single erythrocyte: Comparison of different methods

In this paper we investigate the capabilities of different light scattering programs for light scattering simulation of the single human red blood cell, also known as erythrocyte. Knowledge of the scattering properties can help to solve the inverse problem of classifying erythrocytes according to size and shape using measured scattering diagrams. We compare the different programs by presenting the corresponding scattering diagrams. Then we give an overview of computation times and point out the different characteristics of the methods.     

Theoretical studies on the near field properties of non-concentric core-shell nanoparticle dimers

The concentric core-shell nanoparticle dimers have “hot spots” with enhanced electric fields in their junctions, which can be used in the surface enhanced Raman spectra analysis. Here the non-concentric core-shell nanoparticle dimers are proposed by introducing a shift between the dielectric core and the metal shell. By using the three dimensional finite difference time domain method, the plasmon resonances and the near field properties of the core-shell nanoparticle dimers affected by the non-concentric shift, dimer separation, excitation wavelength and polarization are analyzed in detail. The results show that the local near fields of the non-concentric core-shell nanoparticle dimers can be much more enhanced than those of the concentric ones. Also the plasmon resonance wavelengths of the dimers can be effectively tuned by the non-concentric shifts between the core and shell. The proposed nanostructures can have great potential in various near field applications.     

Electromagnetic scattering by nonspherical particles: Recent advances

This note gives a short introduction to the reprint of the article “Numerical methods in electromagnetic scattering theory” by Kahnert, M (JQSRT 2003;79-80:775-824). Some of the most important developments in the field since the publication of this article are briefly reviewed. A list of typos that have been identified in the original article is given in the appendix.     

Light scattering by Gaussian random ellipsoid particles: First results with discrete-dipole approximation

We introduce the stochastic geometry of a Gaussian random ellipsoid (GE) and, with the discrete-dipole approximation, carry out preliminary computations for light scattering by wavelength-scale GE particles. In the GE geometry, we describe the base ellipsoid by the three semiaxes a?b?c. The axial ratios b:a and c:a appear as two shape parameters additional to those of the Gaussian random sphere geometry (GS). We compare the scattering characteristics of GE particles to those of ellipsoids. Introducing irregularities on ellipsoids smoothens the angular scattering characteristics, in a way analogous to the smoothening of spherical particle characteristics in the case of GS particles.     

Active electric near field imaging of electronic devices

An active two dimensional near field imaging of a High Electron Mobility Transistor (HEMT) used as THz detector has been performed. The reflective imaging system developed at the ENEA FEL Facility in Frascati has been used to this purpose. This imaging technique has shown to be particularly powerful in resolving various coupling mechanisms of the incident radiation with the device.